ANNALS OF THE ORADEA UNIVERSITY
Fascicle of Management and Technological Engineering
ISSUE #1, MAY 2014, http://www.imtuoradea.ro/auo.fmte/
FRICTION PHENOMENON IN POLYAMIDE
– STEEL PLATE FRONT FACE TYPE
CONTACTS
Mihai-Tiberiu LATES1, Catalin GAVRILA2
“Transilvania” University of Brasov, Product Design, Mechatronics and Environment Department, [email protected]
2
“Transilvania” University of Brasov, Product Design, Mechatronics and Environment Department, [email protected]
1
case of small forces.
The applications of polyamide – steel type contacts are
referring mainly in mechanical systems where the
durability of the mechanical contact is an functioning
condition (journal bearings; cams; guides; chain drive
transmissions – the guide/chain contact; taps – the
screw/nut contact; gear transmissions – Fig. 1 presents a
gear made from polyamide, which is part of a solar
tracking system installed at the Transilvania University’s
hill from Brasov, Romania), in the field of mechanical
industry, medicine, machines in food industry [3].
Abstract—The applications of polyamide type mechanical
components are referring on journal bearings, cams, guides,
chain drive transmissions – the guide/chain contact, taps – the
screw/nut contact; gear transmissions. The paper presents the
analysis of the friction phenomenon in polyamide – steel plate
front face type contacts by performing tests on a tribometer test
rig. The results are offering information about the variation of
the sliding friction coefficient, the flatness error and the wear
rat. The conclusions are presenting recommendations regarding
the applications and the functioning conditions of the
polyamide (PA66) type mechanical components.
Keywords—polyamide, friction, steel plate, test.
I. INTRODUCTION
T
HE polyamide type materials are characterized by
high durability due to their good behaviour in the
case of wear functioning conditions; the reason is that,
the polyamide type materials have small friction
coefficients when they are combined with steel materials
in mechanical contacts, high values for the hardness and
high values for the Young’s modulus which allows small
deformations in the case of high forces.
The polyamide materials have high mechanical
strengths for combined stresses, have high stiffness and
are approx. 7.5 times much lighter than the same volume
bronze type materials (anti friction material) but much
cheaper than these [1]. The polyamide type materials are
used in applications with a wide range of temperatures (260oC ... 80oC), with sliding frictions, with high impact
forces, with corrosive environments or with adhesive
working conditions [2].
The mechanical characteristics of the polyamide type
materials are established in literature [1], [2] and show
which are the testing procedures used to determine these
properties and also confirm the high values for the
Young’s coefficient E=2800 - 3300 MPa and for the
density =1.14 - 1.16 kg/m3. The references [1], [2]
present that the mechanical behaviour of the polyamide
type material could be approximated as an elastically
one, in the same range as for a steel type material, in the
Fig. 1. Solar tracking system with polyamide gear
The references [4]-[6] presents that the polyamide type
materials (PA66) are used in a wide area of chain drive
transmissions (as guide’s materials) due to their good
friction behaviour (dynamic friction coefficients close to
0.1 ... 0.13 [5], [6]). The reason is that an optimization
aim of the chain drive transmission is to reduce the
guide-chain contact friction (the guide-chain friction
represents almost 27% from the total chain drive friction
[7], [8]).
The paper presents the analysis of the friction
phenomenon in the case of the polyamide – steel plate
75
ANNALS OF THE ORADEA UNIVERSITY
Fascicle of Management and Technological Engineering
ISSUE #1, MAY 2014, http://www.imtuoradea.ro/auo.fmte/
Fig. 3. The PA66 disks draft drawing
front face type contacts as application in the case of
guide/chains contacts, cams and gear transmissions and
shows recommendations regarding the functioning
conditions of polyamide – front face type contacts.
The final shape of the machined disk is presented in
the Fig. 4.
II. THE TESTING EQUIPMENTS
The tests should be able to offers results regarding the
values of the dynamic and the static friction coefficients
of the polyamide – steel plate front face type contacts.
The dynamic friction coefficient can be measured during
a continuous relative motion; the value of the static
friction coefficient can be obtained at the beginning of
the relative motion or at the moment that the direction of
the relative motion is changed to the opposite direction.
An experimental equipment which allows these types of
motion is a pin on disk type test rig which can be adapted
for the desired tests; the disk is made from polyamide
type material and the pin is adapted to a holder which
includes the steel plate.
The rough disks are made by PA66 polyamide by
pouring and then are cut in slices – Fig. 2.
Fig. 4. The machined disk
The steel plate holder’s drawing is presented in the
Fig. 5; the steel plate 1 is mounted inside the holder and
is fixed with the clip 2 and with the cap of the screw 3.
The steel plate is positioned with the front face normal to
the holder’s axis in order to create a contact between it
and the PA66 polyamide disk from bellow.
Fig. 2. The PA66 polyamide rough disk
Fig. 5. The drawing of the steel plate holder
The rough disks are machined in order to obtain an
adequate quality of the surface and to achieve the
mounting possibility on the test rig; the draft drawings
are presented in the Fig. 3.
The holder is presented in the Fig.6.
Fig. 6. The holder
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ANNALS OF THE ORADEA UNIVERSITY
Fascicle of Management and Technological Engineering
ISSUE #1, MAY 2014, http://www.imtuoradea.ro/auo.fmte/
Fig. 8. The pin on disk module
The test rig which is used to perform the tests in order
obtain the values of the friction coefficient is a pin on
disk type tribometer – Fig. 7.
The PA66 disk is mounted inside the rotary device
from bellow; the steel plate is mounted in the holder and
is acting with the normal force on the disk.
III. THE TESTS
The tests were performed by acting with a normal
force of 5 N, calculated from the condition of
hydrodynamic friction between the disk and front face of
the steel plate. The disk has a rotation of 500 rpm during
2 hours. Fig. 9 shows the variation of the dynamic
friction coefficient  during the tests.
Fig. 9. The dynamic friction coefficient
According to the Fig. 9 the dynamic friction
coefficient is stabilised after 80 minutes of run-in and its
value is close to 0.1 (0.1028) which is in concordance
with the values of it presented in the references (0.1 ...
0.13 [5], [6]). The stabilisation of the dynamic friction
coefficient is relatively fast, so this means that the
running in period of the polyamide/steel contacts made
mechanical transmissions is short.
The variation of the flatness error e is presented in the
Fig. 10. This error is influencing the shocks and
vibrations in the system; Fig. 10 shows that the flatness
error decreases in time and is stabilised after 60 minutes
of running in at a value of 6 m, which is small and it
has a small influence on the shocks and vibrations.
Fig. 7. The tribometer
The tribometer with its pin on disk module – Fig. 8 –
allows measurements in the range of 0.1 ... 1000 N for
the normal force with a resolution of 50 mN. The disk
rotation can be controlled in the range of 0.001 ... 5000
rpm. The test rig is useful to perform wear tests, friction
coefficient measurements and Stribeck tests.
Fig. 10. The flatness error
Fig. 11 presents the variation of the wear rate w for the
peaks and the holes from the disk’s surface. High wear
rate is obtained for the peaks; the wear rate for the peaks
and the holes from the disk’s surface is stabilised after 80
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ANNALS OF THE ORADEA UNIVERSITY
Fascicle of Management and Technological Engineering
ISSUE #1, MAY 2014, http://www.imtuoradea.ro/auo.fmte/
minutes of running in.
references and its value stabilises relatively fast (after 80
minutes); this shows that the running in period for the
mechanical transmissions which have polyamide type
(PA66) components is short.
The flatness error e, according to the measurements, is
stabilised after 60 minutes of running in at a small value
– 6 m; according to that, the usage of PA66 type
materials in mechanical transmissions induce small
errors with small shocks and vibrations in the
transmissions.
In the first period of running-in, the wear rate w is
relative high (up to 150 m for the peaks on the disk’s
front face) and after this period it decreases dramatically
to almost zero. That assures a constant coefficient of
friction and a small amount of abrasive particles from the
PA66 disk. The tests show that for high rotations (3000
rpm – the Stribeck test) the friction coefficient is still
stabilised at the value of 0.11.
Due to their mechanical properties and due to their
behaviour in mechanical transmissions, the polyamide
(PA66) type mechanical components are suitable to be
used with high efficiency (due to their small friction
coefficients) in mechanical transmissions with small
running-in periods.
Fig. 11. The wear rate
The Stribeck test is performed in order to identify the
lubricated friction when the dynamic friction coefficient
has the minimum value. The rotation of the disk is
variable between 5 ... 3000 rpm and the normal force is 5
N. Fig. 12 shows that the lubricated friction appears at
800 rpm; anyhow, the variation of the dynamic friction
coefficient is small.
REFERENCES
[1]
[2]
Fig. 12. The Stribeck curve
According to the results from the tests the polyamide
(PA66) type mechanical components are suitable to be
used with high efficiency (due to the small value of the
friction coefficient) in mechanical transmissions with
small running-in periods.
[3]
[4]
IV. CONCLUSION
[5]
The polyamide type materials are widely used in
mechanical transmissions due to their resistance to wear
and high resistance to tensile stresses. The applications
of polyamide – steel plate front face type contacts are
referring on journal bearings, cams, guides, chain drive
transmissions – the guide/chain contact, taps – the
screw/nut contact, gear transmissions, all of these
characterised by sliding frictions. The paper presents the
tests results regarding the sliding friction between the
mentioned types of contacts.
The testing methodology presented in the article can
be
applied
to
other
pairs
of
materials
(polyamide/polyamide, metal/metal) and allows the study
of the sliding friction (as it is presented in the paper) and
of the rolling friction – for instance, the upper element
can hold a ball.
The dynamic friction coefficient  for sliding motion
has small values (0.1028), comparable with the
[6]
[7]
[8]
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